An average of four children die each week in England in a system that offers "patently inadequate" standards of care in the networks of schools, care workers and children's homes established to protect them, according to Ofsted.

Councils have systematically failed to learn from the mistakes made in dozens of the most serious cases of child abuse, while too many frontline staff in schools and health centres are still unable to recognise signs of abuse, Ofsted said in a report yesterday. Its verdict comes amid public concern after the death of 17-month-old Baby P in Haringey, north London, who died from 50 injuries despite being in regular contact with child protection officers and medics.

In the first report from Ofsted since it took responsibility in April 2007 for inspecting child protection facilities and assessing procedures, the watchdog raised urgent concerns about the system of serious case reviews, which are launched in the worst cases of abuse to help councils learn from mistakes made in their child protection teams.

Between April 2007 and August this year, local authorities reported 424 serious incidents, including 282 child deaths, 136 cases of serious harm, and six in which the outcome was unknown. One in four involved babies under 12 months.

Of 92 serious case reviews, 38 were rated inadequate and 34 just satisfactory - a rating Ofsted says is not good enough.

This led to serious delays in judging what went wrong in the child protection system in "almost all" of the cases, the report said. In one unnamed example it took a local authority four years to conduct a single serious case review, during which time other children could have come to harm. The report warned that some instances of serious abuse were going unreported by local authorities. One in four did not report a single case for review.

Christine Gilbert, Ofsted's chief inspector, welcomed some improvements but said she was frustrated that too many services were "patently inadequate" and improvement "unacceptably slow".

"Too many vulnerable children are still being let down by the system and we are failing to learn from the worst cases of abuse," she said.

Referring to the Baby P case, she said: "I wish I could guarantee that such a case would never happen again. I can't give that guarantee. Everyone working in child protection has to stop, take stock, and look at what they are doing."

Symptoms of abuse were being missed by frontline staff such as teachers and health workers who were still too ready to "accept at face value" any injuries which could be signs of abuse, she said.

The report found some 8% of children's homes were "shockingly" inadequate, with concerns about children's safety in centres which were failing to vet and train staff properly. Bullying was going unchallenged in 7% of settings.

Procedures designed to ensure staff working with children talk to each other - a recommendation after the death of Victoria Climbié - were poor in many areas. "Consequently, necessary actions may not be taken to reduce the risks to children of sexual exploitation and drug or alcohol misuse."

The report also covered education, and found that while the number of inadequate schools had decreased, there was a "stubborn and persistent" problem of underperformance in secondary schools, with 9% judged inadequate. "There is a strong link across every sector between deprivation and poor quality provision," said Gilbert. "This means that children and families already experiencing relative deprivation face further inequity in the quality of care and support for their welfare, learning and development. In short, if you are poor you are more likely to receive poor services: disadvantage compounds disadvantage."

Michael Gove, the shadow education secretary, said: "This Ofsted report underlines what we have been saying - the education system is failing poorer children. The gap between the privileged and disadvantaged is not being closed. That is why a Conservative government would shift resources to spend more money on the education of pupils from more deprived backgrounds."

Jim Knight, the schools minister, said: "There is a lot of good news in this report for frontline staff who are working hard to improve children's lives, to help them learn and achieve, and to keep them safe. But, as we set out in the Children's Plan, we won't be satisfied until every school and every service is meeting the standards set by the best."

Beverley Hughes, the children's minister, added: "I am pleased that the large majority of children's homes and social care services are doing well. However, I am very concerned that the report says that staff in some services are not equipped to recognise and respond to signs of abuse and neglect. Everybody working with children has a clear duty to keep them safe. There are no excuses for ignorance."

School report

• Almost two-thirds of inspected schools were good or outstanding, but the number of underperforming secondaries remained "stubborn and persistent". Some 9% were judged inadequate and 34% just satisfactory.

• More than one in three lessons in primary schools are not good enough, with teaching described as "pedestrian". In English and maths there is too much focus on short exercises instead of sustained pieces of writing or mathematical inquiries. In science, teachers' poor subject knowledge is the major barrier.

• At 11 children are being "over-prepared" for Sats, squeezing out more interesting lessons. High achievers in particular are given little scope to explore subjects fully.

• In secondaries, children are losing interest and behaving badly because they are not being sufficiently stretched. Teaching is too reliant on worksheets or focused on tests.

• Pupil surveys report that children feel safer at school compared with last year. However, in 28% of schools behaviour is no better than satisfactory: "Some pupils lack respect for adults and their peers and are boisterous and inconsiderate in moving around the school site."

• Services for children in care are "slowly" improving but many are given little say in where they are placed and rarely have support from one social worker for any length of time. Looked-after children routinely get among the worst exam results and are most likely to end up in the criminal justice system.

• Children of asylum seekers get worse all-round services than other children in care.